This invention relates to optical components of a laser, and more particularly, to optical components, such as windows, which are exposed to large photon fluxes in a cold gas region of a gas laser, and may suffer photoreduction as a result of exposure to the photon fluxes.
In almost all gas ion lasers there is a decrease in useful laser power output over the operating life of the laser. This decrease in useful power is accentuated by losses at optical elements, for example, window (or windows) of the laser tube.
With lasers that operate at high gain (such as lasers which lase at some visible light frequencies) losses from optical elements, especially windows, while undesirable, can often be tolerated during the operating life of the tube. However, even with such high gain lasers, eliminating or minimizing such losses is desirable. Eliminating or minimizing optical element (window) losses can extend the useful life of the tube and provide more efficient and precise operation of the tube during its useful life.
With lasers that lase at relatively low gain (such as a laser lasing at certain ultraviolet frequencies) a decrease in useful power, accentuated by losses at, for example, a window, can become very significant.
The plasma arc generated in the tubes of gas ion lasers can produce large photon fluxes which are capable of initiating physical and chemical changes on an optical element surface exposed to the fluxes. More particularly, these photon fluxes are capable of producing photoreduction of the exposed optical element surfaces.
Exemplary materials used for optical elements in such lasers includes but is not limited to crystalline SiO.sub.2, Si, fused SiO.sub.2, sapphire, diamond, BeO, MgF.sub.2, ZnS, ZnSe, BaF.sub.2, CaF.sub.2, diamond like carbon, ytrrium aluminum garnet (YAG), yttrium lithium fluoride (YLF), and the like. These materials often experience physical and chemical changes, particularly photoreduction, on the surface exposed to the photon flux. In the case of windows mounted at the end of a laser tube this occurs on the inside surface of the window. Other optical elements disposed within the interior of the tube itself also are subject to photoreduction.
It would be an advancement in the art to provide laser optical components which would not undergo photoreduction when exposed to large photon fluxes, particularly when the laser is one which generates ultraviolet radiation during operation. Such lasers produce ultraviolet radiation either incidental to or as a part of the beam and include noble gas ion lasers, excimer lasers, CO.sub.2 lasers, free electron lasers, atomic metal vapor lasers, and the like.